text: The reason why the author uses the different languages with different groups is because he feels that will attach uniqueness to that group. In one of his interviews I have read, he stresses that for him, characters are very important and he draws the characters first.
  
  In his interview in Germany, when he was asked the same question he replied as below
  
  
    "As for the Arrancar, I think that Spanish sounds very passionate and
    a little erotic, so it matches their wild lifestyle. German sounds
    cold, harsh and methodic, something that matches the straight-forward
    methods of the Quincys. I would also like to use French at some point,
    because it sounds very elegant. But I can't figure out a good way to
    include it into the story."
  
  
  So I believe, as I said before, that it is to associate some sort of uniqueness to the characters belonging to a particular group.